Simplify font size adjustment
I'd like to ask for the ability to easily adjust all the font sizes at once. Right now, it is fairly difficult for the user to increase the overall font size, because it means adjusting every single font in Preferences/Design/Theme. I'd imagine it to be more user friendly to have a drop-down menu in Preferences/Design with three options (small/normal/large) that apply sensible defaults to the font sizes. Of course, it should still be possible to overwrite these settings and even overwrite the font family and stuff by using the theme.
Alternatively, Gajim could also come with a set of prepared and well-defined themes to do the job.